Liquid-crystal non-linear light modulators using electric and magnetic fields

ABSTRACT

A liquid-crystal unit comprising first and second pieces of flat glass, each coated on one side with a transparent electroconductive oxide coating and each having its so-coated surface rubbed with cotton cloth or the like in one direction, with the two surfaces so rubbed then being spaced about 1/4 to 2 mils apart and with a nematic-phase liquid-crystal material of positive dielectric anisotropy in between, and with the directions of rubbing being oriented substantially perpendicular to each other. Such a liquid-crystal unit has the particular property that when there is no potential applied to the electroconductive coatings and the unit is placed between crossed polarizers, light is transmitted, but the application of but a relatively low voltage across the two above-mentioned coatings, something on the order of 5 volts, will generate an electric field that causes the nematic-phase liquid-crystal material to &#39;&#39;&#39;&#39;untwist,&#39;&#39;&#39;&#39; so that it no longer permits transmission of light through the structure comprising the liquid-crystal unit and the crossed polarizers. The effect is quick-acting and reversible. Conversely, with parallel polarizers stationed to each side of such a unit, the effect is the opposite; with no voltage applied, no light is transmitted through the structure, but the application of sufficient voltage makes light transmission possible. The effect is sufficiently clear-cut and local that it is possible to use glass plates that have the electroconductive oxide coating provided only in certain selected areas thereof, with suitable bus bars or the like running to each, and thereby produce alpha-numeric displays. Logic elements, three-dimensional television, and numerous other applications suggest themselves to those skilled in the art.

1 1 :v t.;/ Umted State Fergason LIQUID-CRYSTAL NON-LINEAR LIGHTMODULATORS USING ELECTRIC AND MAGNETIC FIELDS [75] Inventor: James L.Fergason, Kent, Ohio [73] Assignee: Hoffmann-La Roche Inc., Nutley,

Filed: Jan. 24, 1973 Appl. N0.: 326,565

Related U.S. Application Data OTHER PUBLICATIONS Fergason et al: LiquidCrystals and their Applications, Electra-Technology, Jan. 1970, pp.41-50.

Priman- Eraminer-Edward S. Bauer Attorney, Agent, or FirmSamuel L. Welt;Bernard S. Leon; Mark L. Hopkins [57] ABSTRACT A liquid-crystal unitcomprising first and second [4 1 Nov. 11, 1975 pieces of flat glass,each coated on one side with a transparent electroconductive oxidecoating and each having its so-coated surface rubbed with cotton clothor the like in one direction, with the two surfaces so rubbed then beingspaced about A to 2 mils apart and with a nematic-phase liquid-crystalmaterial of positive dielectric anisotropy in between, and with thedirections of rubbing being oriented substantially perpendicular to eachother. Such a liquid-crystal unit has the particular property that whenthere is no potential applied to the electro-conductive coatings and theunit is placed between crossed polarizers, light is transmitted, but theapplication of but a relatively low voltage across the twoabove-mentioned coatings, something on the order of 5 volts, willgenerate an electric field that causes the nematic-phase liquid-crystalmaterial to untwist. so that it no longer permits transmission of lightthrough the structure comprising the liquidcrystal unit and the crossedpolarizers. The effect is quick-acting and reversible. Conversely, withparallel polarizers stationed to each side of such a unit, the effect isthe opposite; with no voltage applied, no light is transmitted throughthe structure, but the application of sufficient voltage makes lighttransmission possible. The effect is sufficiently clear-cut and localthat it is possible to use glass plates that have the electroconductiveoxide coating provided only in certain selected areas thereof, withsuitable bus bars or the like running to each, and thereby producealpha-numeric displays. Logic elements, three-dimensional television,and numerous other applications suggest themselves to those skilled inthe art.

42 Claims, 3 Drawing Figures U.S. Patent Nov. 11, 1975 FIG. 2.

FIG.

E leetracanductive Transparent Caating FIG. 3.

LIQUID-CRYSTAL NON-LINEAR LIGHT MODULATORS USING ELECTRIC AND MAGNETICFIELDS CROSS-REFERENCE TO RELATED APPLICATION This application is adivision of copending application Ser. No. 113,948 filed Feb. 9, 1971,now abandoned BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to a liquid-crystal unit that comprises a pair ofglass plates, provided with a transparent electroconductive coating oftin oxide or the like and suitably prepared and assembled, with aliquidcrystal composition of positive dielectric anisotropy and nematicat room temperature therebetween. In another aspect, the inventionrelates to structures for the intermittent transmission of light,comprising a liquidcrystal unit of the kind above mentioned and a pairof polarizers. In yet another aspect, the nematic-phase liquid-crystalcompositions of the invention are sandwiched between glass plates thatlack the above-mentioned coatings of transparent electroconductivematerial, but means are provided for generating a magnetic field ofsufficient force to cause the nematic-phase material to untwist, withthe same result as is obtained with the application of an electric fieldof sufficient magnitude. In yet another aspect, the invention concernsthe use of liquid-crystal units or structures of the general kindindicated above, with the electroconductive coating being limited tospecific areas and provided with particular, desired potential supplymeans, so as to generate a desired alpha-numeric display.

2. Description of the Prior Art There are known quite a large number oforganic chemical compounds that will, within a particular temperaturerange, exhibit nematic-phase liquid crystals. These compounds are liquidin the sense that their molecules are neither so dissociated as in a gasnor so tightly bound within a structure as in a solid, but at the sametime they are said to be crystalline, in that there is a particularordering to the orientation of molecules, as is sometimes evidenced bypeculiar optical effects. Organic materials exhibit under certainconditions what are sometimes called a mesomorphic phase, and there aredifferent families of organic-chemical compounds that exhibitmesomorphic phases of different kinds-the cholesteric, the smectic, andthe nematic. These are each characterized by a particular kind ofmolecular orientation. Most of the known nematicphase liquid-crystalmaterials are listed by W. Kast in Landolt and Bornstein, Vol. II, Part2a, 6th Ed., Springer, Berlin (1960), pp. 266-335. The known materialsare not, in the main, suitable for widespread use, since they arenematic only at above about Centigrade or within a temperature rangesomewhat too narrow to suit them for such use.

It is known that when a nematic-phase liquid-crystal material isstationed between pieces of glass that have been rubbed, each of themunidirectionally and on the surface in contact with the nematic-phaseliquid-crystal material, there is thus obtained a liquid-crystal unitwhose optic axis lies in the direction of unidirectional rubbing.

The techniques for placing onto flat glass a transparentelectroconductive coating of tin oxide or indium oxide or the like arequite familiar to persons skilled in the art of making flat glass.Reference may be made to the patents of Tarnapol (U.S. Pat. No.2,694,761) or Saunders (US. Pat. No. 2,648,752). It is appreciated thatif the pieces of glass are to be of relatively large surface extent andevenly spaced substantially throughout same, it is necessary to avoidthe development of any appreciable warpage in the flat glass while thetransparent electroconductive coating is developed thereon. Under thetechnology of about 5 years ago this presented a considerable problem,since the transparent electroconductive coatings then known were nearlyalways developed by spraying a tin-containing solution onto glass thatwas quite hot (about lO00F. such that the glass was at about the pointof warping. However, there has recently been made commercially availableby a major flat-glass producer a kind of flat glass that is understoodto have been produced by vacuum cathode-sputtering onto the glass, whileit remains at quite a lower temperature, a composition that isprincipally indium oxide.

It may be taken as known that there are numerous ways of arrangingpatterns of luminous, transparent, or opaque material so as toconstitute, with suitable selective activation, an alphanumeric display.It may be taken as known how to supply electrical potential to, and thusactivate, patches of electroconductive transparent oxide coatingsituated on pieces of flat glass.

SUMMARY OF THE INVENTION It has been discovered that there exists afamily of materials that exhibit nematic phase at room temperature andat the same time a positive dielectric anisotropy. Moreover, they havethese properties over a substantial temperature range.

It has been discovered, moreover, that it is possible to change theknown light-rotating action of nematicphase liquid-crystal materials bythe action of a suitable electrical or magnetic field, and that thethreshold value for such change occurs at conveniently low appliedvoltage, such as 5 volts, and that the liquid-crystal material respondsrapidly and locally to such change.

It has been found that, in view of modern technology concerning theproduction of pieces of flat glass having thereon electroconductivecoatings that are transparent, one may utilize the two above-mentioneddiscoveries for the production of selective devices for the intermittenttransmission of light, as in, for example, alphanumeric displays andlogic devices.

DESCRIPTION OF THE DRAWINGS A complete understanding of the inventionmay be obtained from the foregoing and following description thereof,taken in conjunction with the appended drawings, in which:

FIG. 1 is a schematic view, in section and not to scale, of aliquid-crystal unit made in accordance with the present invention;

FIG. 2 is a view illustrating a certain feature in the mode ofpreparation of the glass pieces used in a liquidcrystal unit accordingto the invention; and

FIG. 3 is a perspective view, partly schematic, of a structure for theselective transmission of light, made in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the practice of the instantinvention, it is considered highly desirable to use a nematic-phaseliquidcrystal composition that has a considerable temperaturerange-within which it exhibits the nematic phase, such as minus C. toplus 70C., at the same time having a positive dielectric anisotropy. Theimportance of the latter factor is not to be overlooked. A negativedielectric anisotropy implies that with the application of a field, themolecules tend to line up parallel to the major surfaces of the piecesof flat glass between which the liquid-crystal material is contained,rather than perpendicular thereto, as is intended and required inaccordance with the concept of the instant invention, which may beconsidered as involving the phenomenon of causing a relaxation of thetwist of a twisted nematicphase material by the application of suchfield. A substantial number of the known nematic-phase liquidcrystalmaterials have negative dielectric anisotropy.

The problem of finding a suitable mixture of organic chemicals so as toobtain a composition of matter that exhibits at, for example, minus 10Centigrade to plus 70 Centigrade, the needed combination of nematicphase and positive dielectric anisotropy may be solved by compoundingthe following mixture: 40 parts by weight ofbis-(4-n-octyloxybenzal)-2-chlorophenylenediamine, 50 parts by weight ofp-methylbenzal-p'-n-butylaniline, and 10 parts by weight ofpcyanobenzal-p'-n-butylaniline. In the mixture abovementioned, it isconsidered that the last-named compound is the one that imparts theessential positive dielectric anisotropy; the use of it in greateramounts may be expected to lower the value of the threshold voltage thatis required to obtain the needed effect. There is an equation that maybe used to express the threshold voltage, namel v =47 k/Ae where vequals the-threshold voltage in volts,

1r equals 3.1416,

k is an elastic constant having units of dynes, and

A6 is a difference in electrical polarizability for the materialinvolved, parallel versus perpendicular to the long axis of themolecules, expressed in c.g.s. units. For the mixture indicated above,perhaps the principal active ingredient is thep-cyanobenzal-p-n-butylaniline. Its structural formula is:

NEC- C=N-- c,H,

It may be made by refluxing p-cyanobenzaldehyde for about 6 hours withp-n-butylaniline, using methanol as solvent. The preparation is routinefor those skilled in making Schiff bases. After recrystallization frommethanol, the desired compound is obtained in a yield of 80 to 85percent.

The possibility of using analogues or homologs of the particularcompound discussed above in place of it is not to be ruled out, but atthis time the propylaniline is not readily available, and thecorresponding compounds made with methylaniline or ethylaniline aresomewhat less soluble and therefore less desirable. It is consideredthat the effects desired may be obtained with the use of a compound ofthe formula:

where R is a saturated aliphatic alkyl radical having 1 to 12 carbonatoms. The para relationship between the radical R and the remainder ofthe molecule is considered essential.

In the particular mixture mentioned above, the bis-(4-n-octyloxybenzal)-2-chlorophenylenediamine is a low-melting solid,and the p-methylbenzal-p-nbutylaniline is a liquid at room temperature.Those skilled in the art may perceive equivalents for these compounds.It is apparent that the proportions in which they are mixed may beadjusted suitably to influence the operating temperature range of themixtureusing more of the former will give mixture that operates (hasnematic phase and positive dielectric anisotropy) at a lowertemperature, while using more of the latter has the opposite effect. Itmay be gathered from the above discussion that the two compoundsdiscussed in this paragraph comprise the major part of the mixture, withthe cyanobenzalbutylaniline comprising only a minor portion thereof.Indeed, as little as 3 parts by weight in of the cyanobenzalbutylanilineappears to be a proportion effective to yield the desired positivedielectric anisotropy while being compatible with the remainder of themixture. On the other hand. it is desirable to use greater proportionsof the cyanobenzalbutylaniline, since this lowers the threshold value,but there is probably not in most cases any particular advantage in theuse of more than about 40 parts by weight in 100.

Though there has been described above one suitable mixture, there aredoubtless others that will be found useful and it is within the spiritand scope of the invention to use them, as hereinafter described andindicated.

In FIG. 1 of the appended drawings, there is shown a liquid-crystal unit2 that comprises a first piece of flat glass 4 and a second piece offlat glass 6. The drawing is not to scale, and it constitutesacross-sectional view. The major surfaces of the piece 4 are indicatedat 8 and 10 and those of piece 6 at 12 and 14.

Preferably, but not absolutely necessary, there are provided upon themajor surfaces 10 and 12 the coatings l6 and 18, respectively. Coatingsl6 and 18 are thin, transparent, electroconductive coatings, such as theknown tin-oxide or indium-oxide coatings. It should be noted that thesecoatings may, for the purposes of the instant invention, be quite thinand highly resistive, for example, on the order of ohms per unit squareor above, and possibly as high as 5,000 or 10,000 ohms per unit square.This contrasts with requirements for lower resistivity in flatglassprovided with transparent electroconductive coatings for such purposesas heated aircraft windows. If the pieces of flat glass are to berelatively large and uniformly spaced from each other, it is desirablethat the transparent electroconductive coating be of the kind that isapplied at relatively low temperature such as about 500 Fahrenheit by aprocess of cathode-sputtering in vacuum, so that dangers of warpage maybe safely avoided.

Completing the structure of unit 2 are the spacers 20 and a layer 22 ofnematic-phase liquid-crystal material with positive dielectricanisotropy. The spacers may be made of any suitable material, such asoil-resistant double-sided adhesive tape, and have such dimensions as toseparate the surfaces and 12 by approximately V4 to 2 mils. The rapidityof the response of the liquid-crystal unit is influenced by the amountof separation between the surfaces 10 and 12. For a response time on theorder of milliseconds, the separation should be small, such as A mil,whereas if a longer response time is tolerable, the separation may becorrespondingly greater, being possibly as great as about 5 mils. Thespacing may in some instances be as little as 0.1 or 0.05 mil.

The nematic-phase liquid-crystal material comprising the layer 22 ispreferably of the kind hereinabove indicated, namely, one comprisingmajor portions such as to 80 weight percent each ofbis-(4'n-octyloxybenzal)-Z-chlorophenylenediamine andp-methylbenzalp-butylaniline, these making up about 60 to 97 weightpercent of the total composition and the p-cyanoben-Zal-p'-p-butylaniline comprising the remaining 3 to 40 weight percent.The use of substitutes in the same or different proportions is not beingruled out, but for the most part, it is difficult to find a materialthat exhibits the combination of properties principally desired, namely,positive dielectric anisotropy and a board operating-temperature rangethat includes room temperature.

In FIG. 2, there is a view of the pieces 4 and 6 of fiat glass (not toscale, the glass being about one-eighth inch thick). The lines 24 on thesurface 10 indicate a direction of rubbing. The lines 26 on the surface12 have the same significance. In the preparation of a liquid-crystalunit 2, the surfaces 10 and 12 that are to be in contact with thenematic-phase liquid-crystal material 22 are prepared by being strokedor rubbed unidirectionally with, for example, a cotton cloth. Thoseskilled in the art of dealing with nematic-phase, liquidcrystalmaterials have long known that such material tends to align with asurface that has been stroked or rubbed unidirectionally. The practicefor making the liquid-crystal unit 2 comprises rubbing the surfaces 10and 12 as indicated, applying the material 22 to one of the surfaces,and then bringing the surfaces 10 and 12 together. As will be observedfrom FIG. 2, the direction of rubbing on the surfaces 10 is oriented atabout 90 with respect to the rubbing on the surface 12. The effeet isthat there is obtained a twisted nematic structure.

The molecules in a nematic-phase liquid crystal material are each longand straight, and they tend to lie parallel, like logs in a river orstraws in a broom. Their parallelism is statistical, rather than perfectand exact; they are free to move with respect to one another, and thereare some that are at some or another small acute angle with respect tothe main stream, and a few others that are at any given moment in aposition even less consonant with the bulk of the others. A property ofthe nematic-phase materials is that the molecules in the vicinity of arubbed surface tend to align themselves with it. The molecules nearestthe surface 10 are thus inclined to orient themselves parallel with thelines 24, and those nearest the surface 12 are inclined to orientthemselves parallel to the lines 26. The structure is fluid and active;the molecules in between, in the various layers that are parallel to thesurfaces 10 and 12, under conditions of no applied voltage, then arrangethemselves in what may be considered a number of layers of suitableintermediate main-streamdirection, ranging from one close to parallel tothe lines 24 (a short distance from the surface 10) through one at abouta angle with respect to both the lines 24 and the lines 26 (at about themidpoint of the distance between the surfaces 10 and 12) and on to oneclose parallel with lines 26 (a short distance from surface 12). Theeffect of the liquid-crystal unit 2 upon polarized light that impingesupon its surface 8 and is polarized parallel to the lines 24 is that theunit effects a rotation of the plane of polarization of the light as itpasses through the unit, so that the light emanating from the surface 14is plane-polarized parallel to the lines 26. It would not matter if theplane-polarized light impinging upon the surface 8 were polarized inparallel planes that were at some angle with respect to the lines 24;the same effect of rotation of the plane of polarization is obtained.The extent of rotation does not need to be any desired extent ofrotation may be obtained, merely by orienting and corresponding properlythe unidirectionally rubbed surfaces 10 and 12.

To obtain a proper understanding of the invention, it is necessary tounderstand that the action of an electric field may change theabove-described orientation of the molecules. It is possible to classifythe nematicphase materials according to their dielectric anisotropy.Anisotropy means (in one sense) a tendency to assume a directionalityand (in another sense) the property of having adopted suchdirectionality. Theoretically, a material may have a dielectricanisotropy of zero, which means that an electric field has no influenceupon the orientation of the molecules, either to make them perpendicularto it (negative) or parallel to it (positive). The particular materialswith which the instant invention is practiced exhibit a positivedielectric anisotropy, which means that it is possible by theapplication of an electric field of sufficient strength to cause themolecules to foresake their previous orientation and align themselvesparallel to the direction of the electric field. The usual elementaryphysics example of an electric field is that existing between the platesof a condenser, and the situation within the unit 2 of the instantinvention is analogous, with the layers 16 and 18 acting like the platesof the condenser. When there is applied to the layers 16 and 18 asuitable d-c potential, the alignment of the molecules in the material22 becomes parallel to the electric field, i.e., perpendicular to thesurfaces 10 and 12. When plane-polarized light impinges upon the surface8, there is now no rotatory effect; the light emanating from th surface14 remains polarized in the same plane.

What is surprising about the phenomena explained above is that theeffect is so rapid, so local, so revers ible, and so obtainable witheven quite a modest impressed voltage, such as about 5 volts andpossibly less.

Those skilled in the art will understand that in the construction of theunit 2 it is necessary to provide a way to impress the voltage acrossthe layers 16 and 18. These means are indicated schematically in FIG. 1as comprising a battery 28 and lead lines 30 and 32, with the line 32preferably containing a switch 34. Of course, the desired electric fieldmay conceivably be produced in other ways that do not require the use ofthe layers 16 and 18 of transparent, electroconductive material, but theuse of some selectively actuable means for the generation of therequired field is essential to the practice of the invention.

The required field need not necessarily be an electric one, at least interms of the means used to produce it. With the use of a magnetic fieldof sufficient strength and suitable location and orientation, it ispossible to obtain the same effect.

In the embodiments contemplated in the previous paragraph, the magneticfield is applied substantially similar to the layer 22 of nematic-phaseliquid-crystal material. An alternative, of course, is to use anematicphase, liquid-crystal which has positive diamagnetic anisotropy.Most namatic-phase liquid-crystal materials exhibit negative diamagneticanisotropy. When a liquid-crystal material of positive diamagneticanisotropy is used, the effect of the magnetic field may be reinforcedby the application of an electric field.

Bearing in mind the foregoing, there will be explained below withreference to FIG. 3 how, by means of a structure 36 the light emanatingfrom a source 38 may be allowed to reach or prevented from reaching aneye 40 or other light-sensitive device, all in accordance with themanipulation of a switch 42. The structure 36 comprises a liquid-crystalunit 2, sandwiched between crossed polarizers 44 and 46. The switch 42corresponds to the switch 34 of FIG. 1, and the battery 48 correspondsto the battery 28. With the light source 38 operating constantly, lightpasses through the polarizer 44 and becomes plane-polarized. With noapplied voltage, the unit 2 rotates the plane of polarization of thelight passing therethrough through 90, so that the light is nowplane-polarized in such a manner as to be passed by the polarizer 46.Thus, the light is received by the eye 40.

When the switch 42 is closed, there is a change within the unit 2 asabove described, such that its effect of rotating the plane ofpolarization disappears, and the light passes straight through the unit2, coming against the polarizer 46, whose plane to polarization iscrosswise of that of the light impinging upon it-hence, no transmission.The effect is rapid, requiring at most a few seconds and possiblysomething on the order of milliseconds. It is local; those skilled inthe art will readily appreciate how suitable alphanumeric displays maybe generated, merely by using suitably shaped and located and poweredsegments of electroconductive coating in place of the above-describedlayers 16 and 18.

In the foregoing description, the polarizers 44 and 46 are crossed, butit will be apparent to those skilled in the art what would happen ifthey were parallel. The structure would then operate in just the reversemanner: with no applied voltage, no transmission and with appliedvoltage, transmission.

Devices more complex can be made. For example, with three polarizers andtwo units, one can make an AND gate. If the polarizers are all paralleland the parts are arranged polarizer-unit-polarizer-unit-polarizer, thefailure to activate one or both of the units by applying voltage willcause the gate to fail to transmit.

As another example, one can make an exclusive NOR gate, using twoparallel polarizers and first and second units between them. This gatewill not transmit if one unit or the other is activated, but it will ifboth or neither is activated.

The design of other and more complicated kinds of logic devicesinvolving larger numbers of units in logical-zero or logical-onecondition, is also possible.

Numerous other potential applications of the instant invention suggestthemselves to those skilled in the art. Boolean-function generators maybe made in this way. The devices may be used for shuttering. With asystem sufficiently fast-acting, it is possible to generatethreedimensional television or movie images (though, as before, glassespolarized in different directions must be worn) by suitable rapid andrepeated activation or deactivation of the electric field.

Although there has been disclosed hereinabove a practice of preparingthe surfaces that are to come into contact with the liquid material bystroking or rubbing with a cotton cloth, it will be apparent to thoseskilled in the art that as the art develops, it is likely that variousmeans more sophisticated and effective for preparing the surfaceinvolved will be developed. The technique of preparing the plates eitherby stroking or rubbing or by more sophisticated means to effectappropriate alignment of the liquid crystal molecules at the facingsurfaces of the plates, is known as wall orientation." Thus, wallorientation denotes a certain surface state exerting an orientinginfluence on the molecules adjacent to the plates, i.e. on the boundarylayer of the liquid crystal, which causes the liquid crystal to define atwisted structure.

In the disclosure contained hereinabove, there is contemplated only thepossibility that the polarizers used may be elements external to theliquid-crystal unit. It is possible, however, to incorporate thepolarizers directly into the unit. This may be done by treating thesurfaces of the conductive coating, after it has been rubbed, with asolution which forms a dichroic film of the kind described by Dryer inUS. Pat. Nos. 2,544,659, 2,524,286 and 2,400,877. A suitable solutioncomprises a 4 weight percent aqueous solution of methylene blue.

Those skilled in the art of constructing multipoint visual displays willpreceive that it is possible with the use of the instant invention tosimplify considerably the problem of addressing a plurality of points.Instead of requiring 35 separate inputs for a five-by seven alphanumericdisplay, the same result can be accomplished with only 12 inputs, onefor each row and one for each column.

I claim as my invention:

1. An optical device for continuous control of light transmissioncomprising:

electro-optical cell means including liquid crystal means havingpositive dielectric anisotropy disposed between two spaced plates, atleast one of which plates is transparent and each plate beingelectrically conductive at a surface facing said liquid crystal means;

said plates being wall-oriented to cause said liquid crystal means todefine a twisted structure in the direction perpendicular to the plates;

polarizing means disposed one before and one behind the liquid crystalmeans, in the direction of light traveling through the cell means; and

electrical means connected to the plates for controlling the twistedstructure of said liquid crystal means.

2. An optical device according to claim 1 wherein said liquid crystalmeans has a nematic phase which includes room temperature.

3. An optical device according to claim 1 wherein said liquid crystalmeans has a nematic phase in the temperature range of at least l0C to C.

4. An optical device according to claim 2 wherein said polarizing meanscomprises dichroic films.

5. An optical device according to claim 4 wherein the surfaces of theplates facing the liquid crystal means are covered with a film of atransparent conductive material and wherein said dichroic films aredeposited on 9 said films of conductive material and are in contact withsaid liquid crystal means.

6. An optical device according to claim wherein both plates aretransparent.

7. An optical device according to claim 2 wherein the plates have atransparent conductive material on each of said facing surfaces and saidelectrical means includes connecting leads in operative contact with theconductive material for applying a voltage to the plates,

said electrical means being adapted to apply an electril cal fieldacross the liquid crystal means perpendicular to the plates.

8. An optical device according to claim 1 wherein said facing surfacesof the plates are unidirectionally rubbed in non-parallel directionsrelative to one another.

9. An optical device according to claim 8 wherein said surfaces of theplates are rubbed unidirectionally at right angles to each other.

10. An optical device according to claim 9 wherein the two polarizingmeans are oriented parallel to one another.

11. An electro-optical device according to claim 9 wherein said twopolarizing means are crossed.

12. An optical device according to claim 9 wherein said plates arespaced 0.05 to 5 mils apart.

13. An optical device according to claim 2 wherein said liquid crystalmeans consists essentially of a nematic liquid crystal material.

14. An optical cell for continuously passing substantially all incidentpolarized light comprising:

two plates at least one of which plates is transparent;

a substance between the plates consisting of a mixture of nematic liquidcrystals, said mixture having positive dielectric anisotropy; saidplates being wall oriented in non-parallel directions relative to oneanother for causing said mixture to define a twisted structure in adirection substantially perpendicular to the plates; and

electrical means for providing an electrical field across said liquidcrystal mixture transverse to the plates for controlling the twistedstructure of said mixture.

15. An optical cell according to claim 14 wherein said liquid crystalmixture is in its nematic phase at room temperature.

16. An optical cell according to claim 15 wherein said electrical meansincludes conductive means comprising a transparent conductive materialon the facing surfaces of said plates and connecting leads for applyinga voltage to the plates.

17. An optical cell according to claim 16 wherein the surfaces of theplates facing the liquid crystal mixture are each at least partiallycovered with said transparent conductive material and wherein theconnecting leads are established for the purpose of applying voltage tothe conductive material.

18. An optical cell according to claim 17 wherein both plates aretransparent.

19. An optical cell according to claim 18 wherein the surfaces of theplates facing the liquid crystal mixture are rubbed to effect said wallorientation.

20. An optical cell according to claim 19 wherein the plate surfaceshave a preferential direction.

21. An optical cell according to claim 18 wherein said surfaces of theplates are rubbed unidirectionally at right angles to each other.

10 22. An optical cell according to claim 15 wherein the wallorientation resides in a surface state of the plates exerting anorienting action on the molecules of the nematic liquid crystal mixture.

23. An optical cell according to claim 22 wherein said plates are spaced0.05 to 5 mils apart.

24. A process for the control of light transmission comprising the stepsof:

providing an electro-optical cell having nematic liquid crystal means ofpositive dielectric anisotropy disposed between a pair of spaced platesat least one of which is transparent and means for enabling anelectrical field to be applied across the liquid crystal means, saidplates being wall oriented at the surface thereof facing the liquidcrystal means to cause said liquid crystal means to define a twistedstructure in the direction perpendicular to the plates;

polarizing, with a first polarizing means, light entering the cellwhereby the direction of polarization of polarized light transmittedthrough the liquid crystal means follows the orientation of themolecules of the liquid crystal means;

providing transverse to said plates the electric field across at least aportion of the liquid crystal means for changing the orientation of theliquid crystal molecules under the influence of the electrical fieldsuch that said molecules align in a direction substantially parallel tothe direction of the electric field; and

analyzing with a second polarizing means light transmitted through theliquid crystal means.

25. A process according to claim 24 wherein said field is a DC field.

26. A process according to claim 24 wherein said field is an alternatingfield.

27. A process according to claim 24 including rubbing each of saidfacing surfaces to derive a surface state oriented in a non-paralleldirection relative to one another.

28. A process according to claim 27 wherein the surface state of eachfacing surface is oriented in a direction which is perpendicular to thedirection of orientation of the other, such that the plane ofpolarization of the light is rotated through 29. A process according toclaim 24 wherein said liquid crystal means consists essentially of anematic liquid crystal material.

30. A process according to claim 29 wherein said liquid crystal means isnematic at room temperature.

31. A method for controlling light transmission comprising:

providing an optical cell having a pair of spaced plates, at least oneof which is transparent, nematic liquid crystal means of positivedielectric anisotropy disposed between said plates and means forenabling an electrical field to be applied across the liquid crystalmeans, the surfaces of the plates facing the liquid crystal means eachhaving a surface state oriented in a non-parallel direction relative toone another, the surface state of the facing surfaces exerting anorienting influence on the molecules of the liquid crystal means suchthat the molecules define a structure which rotates the plane ofpolarization of substantially all of the light passing through theliquid crystal means in the absence of the electric field;

polarizing, with a first polarizing means, light entering the cellwhereby the direction of polarization of polarized light passing throughthe liquid crystal means follows the orientation of the molecules of theliquid crystal means;

providing transverse to said plates the electric field across at least aportion of the liquid crystal means for changing the orientation of theliquid crystal molecules which are under the influence of the electricalfield such that said molecules align in a direction substantiallyparallel to the direction of the electric field, and light passingthrough said portion follows the orientation of said influencedmolecules; and

analyzing with a second polarizing means light transmitted through theliquid crystal means.

32. A method according to claim 31 wherein the surface state of eachfacing surface is oriented in a direction which is perpendicular to thedirection of orientation of the other, such that the plane ofpolarization of the light is rotated through 90.

33. An optical device comprising:

a. optical cell means comprising a pair of spaced plates, at least oneof which is transparent and a substance disposed between said plateswhich passes substantially all light incident on the substance and whichconsists essentially of a nematic liquid crystal material of positivedielectric anisotropy, said substance having a molecular orientationdefining a structure which optically rotates substantially all lightpassing through the substance, the surface of each plate facing thesubstance having a surface state oriented in a non-parallel directionrelative to one another, for causing the molecules of the substance tobecome oriented into said structure;

b. means in operative contact with the substance for electricallycontrolling the molecular orientation of at least a portion of thesubstance effective to terminate the optical rotation of the lightpassing through the electrically controlled portion of the substance;

c. means proximate said at least one transparent plate for polarizingthe light received by said transparent plate; and

d. polarizing means proximate the other of said plates for analyzing thelight passing throughthe substance.

34. An optical device according to claim 33 wherein the liquid crystalmaterials is in its nematic phase at room temperature.

35. An optical device according to claim 34 wherein said means forelectrically controlling the molecular orientation of said portion ofthe substance includes conductive means comprising a transparentconductive material on the facing surfaces of said plates and connectingleads for applying a voltage to the plates.

36. An optical device according to claim 34 wherein said facing surfacesare unidirectionally rubbed in nonparallel directions relative to oneanother to provide said surface state.

37. An optical device according to claim 36 wherein said facing surfaceis rubbed in a direction which is perpendicular to the direction ofrubbing of the other.

38. An optical device according to claim 33 wherein the liquid crystalmaterial is nematic in the temperature range of at least C to 70C.

39. An optical device for controlling the transmission of lightcomprising:

a. a substance consisting essentially of a nematic liquid crystalmaterial having positive dielectric anisotropy,

b. means confining said liquid crystal material whereby said confiningmeans and said liquid crystal material form an optical cell which passesthrough the liquid crystal material substantially all light incident onthe liquid crystal material,

c. said liquid crystal material having a twisted molecular structure,

d. said confining means being transparent on at least one side of saidcell and being prepared at the surfaces facing the liquid crystalmaterial to cause said liquid crystal material to define said twistedstructure wherein the twist extends in a direction transverse to said atleast one side of said cell,

e. light polarizing means disposed in front of and behind the liquidcrystal material in the path of light transmitted through the liquidcrystal material, and

f. means for applying an electrical field to said liquid crystalmaterial to control its twisted structure.

40. An optical device according to claim 39 wherein said liquid crystalmaterial has a nematic phase in the temperature range of at least -10Cto C.

41. A device according to claim 40 wherein said means for applying anelectrical field includes conductive material on said facing surfacesand means for applying a voltage to the conductive material andestablishing said electrical field across at least a portion of saidliquid crystal means whereby the molecules of the liquid crystal meansunder the influence of the electrical field align substantially parallelto the direction of the applied electrical field.

42. A method of controlling the transmission of light comprising thesteps of:

a. confining a nematic liquid crystal material having positivedielectric anisotropy between a pair of facing wall surfaces at leastone of which walls is transparent,

b. establishing a first condition of light transmission in the liquidcrystal material by preparing said facing wall surfaces to provide asurface state oriented in non-parallel directions relative to oneanother for causing the liquid crystal material to assume a molecularorientation effective to rotate the plane of polarized light through apredetermined angle,

c. introducing polarized light into the liquid crystal material throughsaid at least one transparent wall and in said first condition rotatingthe plane of polarization of the light through said predetermined angleas it passes through the liquid crystal material,

d. directing the rotated light to a polarizer having a plane ofpolarization in predetermined relationship with the plane ofpolarization of the light incident on the liquid crystal material,

e. electrically establishing a second condition in at least a portion ofthe liquid crystal material such that the plane of polarization of lightemitted therefrom is transverse to the plane of polarization of emittedlight from the liquid crystal material in said first condition, and

f. transmitting light from said polarizer when said portion of theliquid crystal material is in one of said conditions and substantiallyblocking the transmission of light by said polarizer when said portionof the liquid crystal material is in the other of said conditions.

Disclaimer 3,918,796.James L. Fey-gason, Kent, Ohio, LIQUID-CRYSTAL NON-LINEAR LIGHT MODULATORS USING ELECTRIC AND MAGNETIC FIELDS. Patent datedNov. 11, 1975. Disclaimer filed July 2, 1976, by the assignee, Hoflmcmn-La Roche Inc. The term of this patent subsequent to May 8, 1990has been disclaimed.

[Oflicial Gazette Febmwy 8, 1.977.]

1. An optical device for continuous control of lght transmissioncomprising: electro-optical cell means including liquid crystal meanshaving positive dielectric anisotropy disposed between two spacedplates, at least one of which plates is transparent and each plate beingelectrically conductive at a surface facing said liquid crystal means;said plates being wall-oriented to cause said liquid crystal means todefine a twisted structure in the direction perpendicular to the plates;polarizing means disposed one before and one behind the liquid crystalmeans, in the direction of light traveling through the cell means; andelectrical means connected to the plates for controlling the twistedstructure of said liquid crystal means.
 2. An optical device accordingto claim 1 wherein said liquid crystal means has a nematic phase whichincludes room temperature.
 3. An optical device according to claim 1wherein said liquid crystal means has a nematic phase in the temperaturerange of at least -10*C to 70*C.
 4. An optical device according to claim2 wherein said polarizing means comprises dichroic films.
 5. An opticaldevice according to claim 4 wherein the surfaces of the plates facingthe liquid crystal means are covered with a film of a transparentconductive material and wherein said dichroic films are deposited onsaid films of conductive material and are in contact with said liquidcrystal means.
 6. An optical device according to claim 5 wherein bothplates are transparent.
 7. An optical device according to claim 2wherein the plates have a transparent conductive material on each ofsaid facing surfaces and said electrical means includes connecting leadsin operative contact with the conductive material for applying a voltageto the plates, said electrical means being adapted to apply anelectrical field across the liquid crystal means perpendicular to theplates.
 8. An optical device according to claim 1 wherein said facingsurfaces of the plates are unidirectionally rubbed in non-paralleldirections relative to one another.
 9. An optical device according toclaim 8 wherein said surfaces of the plates are rubbed unidirectionallyat right angles to each other.
 10. An optical device according to claim9 wherein the two polarizing means are oriented parallel to one another.11. An electro-optical device according to claim 9 wherein said twopolarizing means are crossed.
 12. An optical device according to claim 9wherein said plates are spaced 0.05 to 5 mils apart.
 13. An opticaldevice according to claim 2 wherein said liquid crystal means consistsessentially of a nematic liquid crystal material.
 14. An optical cellfor continuously passing substantially all incident polarized lightcomprising: two plates at least one of which plates is transparent; asubstance between the plates consisting of a mixture of nematic liquidcrystals, said mixture having positive dielectric anisotropy; saidplates being wall oriented in non-parallel directions relative to oneanother for causing said mixture to define a twisted structure in adirection substantially perpendicular to the plates; and electricalmeans for providing an electrical field across said liQuid crystalmixture transverse to the plates for controlling the twisted structureof said mixture.
 15. An optical cell according to claim 14 wherein saidliquid crystal mixture is in its nematic phase at room temperature. 16.An optical cell according to claim 15 wherein said electrical meansincludes conductive means comprising a transparent conductive materialon the facing surfaces of said plates and connecting leads for applyinga voltage to the plates.
 17. An optical cell according to claim 16wherein the surfaces of the plates facing the liquid crystal mixture areeach at least partially covered with said transparent conductivematerial and wherein the connecting leads are established for thepurpose of applying voltage to the conductive material.
 18. An opticalcell according to claim 17 wherein both plates are transparent.
 19. Anoptical cell according to claim 18 wherein the surfaces of the platesfacing the liquid crystal mixture are rubbed to effect said wallorientation.
 20. An optical cell according to claim 19 wherein the platesurfaces have a preferential direction.
 21. An optical cell according toclaim 18 wherein said surfaces of the plates are rubbed unidirectionallyat right angles to each other.
 22. An optical cell according to claim 15wherein the wall orientation resides in a surface state of the platesexerting an orienting action on the molecules of the nematic liquidcrystal mixture.
 23. An optical cell according to claim 22 wherein saidplates are spaced 0.05 to 5 mils apart.
 24. A process for the control oflight transmission comprising the steps of: providing an electro-opticalcell having nematic liquid crystal means of positive dielectricanisotropy disposed between a pair of spaced plates at least one ofwhich is transparent and means for enabling an electrical field to beapplied across the liquid crystal means, said plates being wall orientedat the surface thereof facing the liquid crystal means to cause saidliquid crystal means to define a twisted structure in the directionperpendicular to the plates; polarizing, with a first polarizing means,light entering the cell whereby the direction of polarization ofpolarized light transmitted through the liquid crystal means follows theorientation of the molecules of the liquid crystal means; providingtransverse to said plates the electric field across at least a portionof the liquid crystal means for changing the orientation of the liquidcrystal molecules under the influence of the electrical field such thatsaid molecules align in a direction substantially parallel to thedirection of the electric field; and analyzing with a second polarizingmeans light transmitted through the liquid crystal means.
 25. A processaccording to claim 24 wherein said field is a DC field.
 26. A processaccording to claim 24 wherein said field is an alternating field.
 27. Aprocess according to claim 24 including rubbing each of said facingsurfaces to derive a surface state oriented in a non-parallel directionrelative to one another.
 28. A process according to claim 27 wherein thesurface state of each facing surface is oriented in a direction which isperpendicular to the direction of orientation of the other, such thatthe plane of polarization of the light is rotated through 90*.
 29. Aprocess according to claim 24 wherein said liquid crystal means consistsessentially of a nematic liquid crystal material.
 30. A processaccording to claim 29 wherein said liquid crystal means is nematic atroom temperature.
 31. A method for controlling light transmissioncomprising: providing an optical cell having a pair of spaced plates, atleast one of which is transparent, nematic liquid crystal means ofpositive dielectric anisotropy disposed between said plates and meansfor enabling an electrical field to be applied across the liquid crystalmeans, the surfaces of the plates facing the liquid crystal means eachhaving a sUrface state oriented in a non-parallel direction relative toone another, the surface state of the facing surfaces exerting anorienting influence on the molecules of the liquid crystal means suchthat the molecules define a structure which rotates the plane ofpolarization of substantially all of the light passing through theliquid crystal means in the absence of the electric field; polarizing,with a first polarizing means, light entering the cell whereby thedirection of polarization of polarized light passing through the liquidcrystal means follows the orientation of the molecules of the liquidcrystal means; providing transverse to said plates the electric fieldacross at least a portion of the liquid crystal means for changing theorientation of the liquid crystal molecules which are under theinfluence of the electrical field such that said molecules align in adirection substantially parallel to the direction of the electric field,and light passing through said portion follows the orientation of saidinfluenced molecules; and analyzing with a second polarizing means lighttransmitted through the liquid crystal means.
 32. A method according toclaim 31 wherein the surface state of each facing surface is oriented ina direction which is perpendicular to the direction of orientation ofthe other, such that the plane of polarization of the light is rotatedthrough 90*.
 33. An optical device comprising: a. optical cell meanscomprising a pair of spaced plates, at least one of which is transparentand a substance disposed between said plates which passes substantiallyall light incident on the substance and which consists essentially of anematic liquid crystal material of positive dielectric anisotropy, saidsubstance having a molecular orientation defining a structure whichoptically rotates substantially all light passing through the substance,the surface of each plate facing the substance having a surface stateoriented in a non-parallel direction relative to one another, forcausing the molecules of the substance to become oriented into saidstructure; b. means in operative contact with the substance forelectrically controlling the molecular orientation of at least a portionof the substance effective to terminate the optical rotation of thelight passing through the electrically controlled portion of thesubstance; c. means proximate said at least one transparent plate forpolarizing the light received by said transparent plate; and d.polarizing means proximate the other of said plates for analyzing thelight passing through the substance.
 34. An optical device according toclaim 33 wherein the liquid crystal materials is in its nematic phase atroom temperature.
 35. An optical device according to claim 34 whereinsaid means for electrically controlling the molecular orientation ofsaid portion of the substance includes conductive means comprising atransparent conductive material on the facing surfaces of said platesand connecting leads for applying a voltage to the plates.
 36. Anoptical device according to claim 34 wherein said facing surfaces areunidirectionally rubbed in non-parallel directions relative to oneanother to provide said surface state.
 37. An optical device accordingto claim 36 wherein said facing surface is rubbed in a direction whichis perpendicular to the direction of rubbing of the other.
 38. Anoptical device according to claim 33 wherein the liquid crystal materialis nematic in the temperature range of at least -10*C to 70*C.
 39. Anoptical device for controlling the transmission of light comprising: a.a substance consisting essentially of a nematic liquid crystal materialhaving positive dielectric anisotropy, b. means confining said liquidcrystal material whereby said confining means and said liquid crystalmaterial form an optical cell which passes through the liquid crystalmaterial substantially all light incident on the liquid crystalmaterial, c. said liquid crystal material having a twisted molecularstructure, d. said confining means being transparent on at least oneside of said cell and being prepared at the surfaces facing the liquidcrystal material to cause said liquid crystal material to define saidtwisted structure wherein the twist extends in a direction transverse tosaid at least one side of said cell, e. light polarizing means disposedin front of and behind the liquid crystal material in the path of lighttransmitted through the liquid crystal material, and f. means forapplying an electrical field to said liquid crystal material to controlits twisted structure.
 40. An optical device according to claim 39wherein said liquid crystal material has a nematic phase in thetemperature range of at least -10*C to 70*C.
 41. A device according toclaim 40 wherein said means for applying an electrical field includesconductive material on said facing surfaces and means for applying avoltage to the conductive material and establishing said electricalfield across at least a portion of said liquid crystal means whereby themolecules of the liquid crystal means under the influence of theelectrical field align substantially parallel to the direction of theapplied electrical field.
 42. A method of controlling the transmissionof light comprising the steps of: a. confining a nematic liquid crystalmaterial having positive dielectric anisotropy between a pair of facingwall surfaces at least one of which walls is transparent, b.establishing a first condition of light transmission in the liquidcrystal material by preparing said facing wall surfaces to provide asurface state oriented in non-parallel directions relative to oneanother for causing the liquid crystal material to assume a molecularorientation effective to rotate the plane of polarized light through apredetermined angle, c. introducing polarized light into the liquidcrystal material through said at least one transparent wall and in saidfirst condition rotating the plane of polarization of the light throughsaid predetermined angle as it passes through the liquid crystalmaterial, d. directing the rotated light to a polarizer having a planeof polarization in predetermined relationship with the plane ofpolarization of the light incident on the liquid crystal material, e.electrically establishing a second condition in at least a portion ofthe liquid crystal material such that the plane of polarization of lightemitted therefrom is transverse to the plane of polarization of emittedlight from the liquid crystal material in said first condition, and f.transmitting light from said polarizer when said portion of the liquidcrystal material is in one of said conditions and substantially blockingthe transmission of light by said polarizer when said portion of theliquid crystal material is in the other of said conditions.